Circuitry for superimposing small, low energy signals and large, essentially higher energy signals

ABSTRACT

A circuitry is disclosed for superimposing small, low energy (2) and large substantially higher energy (3) signals, in particular for transmitting speech signals with a remote supply direct signal for a receiving circuit or with a high energy alternating signal, for example a call alternating voltage for signaling. The circuitry includes an operational amplifier (1), having one input connected to a pole of a source supplying the small signal and operational voltage inputs being connected to a voltage supply source. In order to allow low energy, weak signals, such as speech signals, and high energy signals and direct voltages to be transmitted by such a circuitry over a subscriber line by means of simple components, the second pole of the small signal source (2) is connected to the second input of the operational amplifier (1) and one pole of a higher energy signal supply source (3) is connected to one pole of the voltage supply source (V).

The invention refers to a circuitry for superimposing small, low energyand large, essentially higher energy signals, in particular fortransmitting speech signals with a direct signal for the remote supplyof a receiving circuit or with a high energy alternating signal, e.g. acall alternating voltage for signaling, with the circuitry including anoperational amplifier having one input connected to a pole of a sourcesupplying the small signal and operational voltage inputs connected to avoltage supply source.

Currently, the superimposition e.g. of speech signals and supply voltageis mostly attained with the aid of a transformer, with the e.g. one callalternating voltage being actually supplied in a telephone system via arelay to the subscriber lines. During this time, the speech signalsource is completely separated from the subscriber lines. Sincetransformers as well as relays are relatively large and expensivecomponents and especially relays as mechanical components are highlysusceptible to wear, the use of such components results in respectivedrawbacks.

With the conventional SLIC (subscriber line interface circuit), asolution of this problem is proposed in the manner that the subscriberlines are activated by integrated amplifiers whereby the output voltagearea of these amplifiers must contain the entire small and large signalcontrol range of the subscriber line. The switching circuits musttherefore be built in accordance with a technology in which the electricstrength has to correspond to the greatest occurring signal. Typically,these are 48 V to 60 V for the remote supply and up to 180 V_(pp), forthe call alternating voltage, whereupon the speech alternating voltagelies in the area of 2-3 V_(pp). This realization however resultsnecessarily in the drawback of a very great power loss at the 180 Voperational amplifiers whereby the required electric strengthnecessitates the use of very large transistors so that only very fewfunctions can be integrated on a chip of acceptable dimension.

It is an object of the invention to eliminate these drawbacks and topropose a circuitry of the above-stated type by which the transmissionof low energy, weak signals, e.g. speech signals and high energy signalsand direct voltages to a subscriber line is possible in a simple mannerwithout requiring transformers and relays and without using especiallyvoltage-stable operational amplifiers.

In accordance with the invention, this is attained by connecting thesecond pole of the source supplying the low energy signals with thesecond input of the operational amplifier and by connecting a pole of asource supplying a high energy signal with a pole of the supply voltagesource.

These measures make it e.g. possible to control one or both conductorsof a subscriber line in a telephone system with operational amplifiers,with its control range and thus also with its supply voltage, whichessentially determines the occurring power loss, being suited only tothe occurring small signals e.g. the speech signal, and being insulatedfrom the remaining circuitry components such that their supply voltagereference potential can be connected with a source of the high energysignals.

The transmission of the speech signals to the differential voltageinputs of the insulated amplifier or amplifiers may thereby be randomlymodulated or unmodulated e.g. capacitively, galvanically or optically,either analog or digital.

For increasing the voltage modulation capability of an operationalamplifier, it has also been already proposed to relate the supplyvoltage to the outlet voltage, with the supply voltage source beinglinked to the outlet of the operational amplifier.

According to a further feature of the invention, it may be provided tolink one pole of the source supplying the high energy signals with aninput of the operational amplifier with which also one pole of thesupply voltage source is in communication.

These measures result in a very simple structure of the circuitryaccording to the invention.

Furthermore, it may also be provided to connect one pole of the sourcesupplying the high energy signals with an operational voltage input ofthe operational amplifier.

This results in a superimposition of the supply voltage with the highenergy signals.

According to a further feature of the invention, it may be provided toform the source supplying the high energy signals by a clocked voltagetransformer which has a control input receiving a control signal.

In this manner, the source for the high energy signals is highlyefficient, without requiring special structural designs of coolingbodies.

The invention will now be explained in more detail with reference to thedrawing in which:

FIG. 1 shows schematically a first embodiment of a circuitry accordingto the invention,

FIG. 2 shows a further embodiment of a circuitry according to theinvention, and

FIG. 3 shows schematically a source for generating a high energy signal.

In the embodiment according to FIG. 1, a signal source 2 for generatingsmall, low energy signals is connected to both signal inputs + and - ofan operational amplifier 1 with preset amplification, with a resistor R1being interposed. Furthermore, a source 3 for supplying high energysignals is connected with one of its poles to the signal inlet + of theoperational amplifier 1.

Also linked to this input + of the operational amplifier 1 are the onepoles of two supply voltage sources V1, V2 to thereby relate the supplyvoltage to the input of the operational amplifier 1.

The output of the operational amplifier 1 is fed back via a resistor R2to the inverting input-.

The output voltage U_(a) is tapped against the reference potential ofthe source 3 for supply of the high energy signals.

In the embodiment according to FIG. 2, the source 2 for supplying thelow energy signals is also connected to the inverting input - and thenon-inverting input of the operational amplifier 1. The source 3 forsupplying the high energy signals is however linked in this embodimentwith an operational voltage input of the operational amplifier 1, whichinput is also linked to a pole of a supply voltage source V, the secondpole of which being connected to the second operational voltage input ofthe operational amplifier 1.

Also in this embodiment, the delivery of the output voltage U_(a) occursagainst the reference potential of the source 3 for supplying the highenergy signals.

An example of a source 3 for supplying high energy signals isillustrated in FIG. 3.

In this embodiment, a signal source 4 which supplies weak signalscontrols a pulse-width modulator 5 which controls the switches 6 and 7,usually designed as electronic switches, of a clocked voltagetransformer 8. This voltage transformer may be of random design. In theillustrated embodiment, the voltage transformer 8 is formed through aseries connection of a choke 9 and a capacitor 10, with the amplifiedsignal voltage being tapped at the point of connection of the choke 9with the capacitor 10 against a reference potential.

We claim:
 1. A circuitry for superimposing a small, low energy signalfrom a first source and large, essentially higher energy signals from asecond source, the first and second sources each having respective firstand second poles, more particularly for transmitting speech signals witha direct signal for remotely supplying a load comprising a receivingcircuit or with a high energy alternating signal, with the circuitryincluding an operational amplifier having first and second inputs,having the first input connected to a first pole of the first source,and having supply voltage inputs connected to a voltage supply source,characterized in that a second pole of the first source is connectedwith the second input of the operational amplifier and in that one poleof the second source is connected with a pole of the voltage supplysource.
 2. Circuitry according to claim 1, characterized in that one ofthe poles of the second source is connected with an input of theoperational amplifier and is further coupled to one of the poles of thevoltage supply source.
 3. Circuitry according to claim 1, characterizedin that one of the poles of the second source is connected with one ofthe supply voltage inputs.
 4. Circuitry according to claim 1,characterized in that the second source comprises a clocked voltagetransformer which has a control input receiving a control signal.
 5. Acircuit arrangement for transmitting to a remote receiver a relativelysmall audio signal voltage including a DC component of a given value,and a relatively large alternating signal voltage, said circuitarrangement comprising an operational amplifier having a differentialinput, an output, and a pair of power supply terminals for receivingtherebetween an operating voltage from a power supply, whereinsaid audiosignal voltage is applied in a differential mode to said differentialinput; and said alternating signal voltage is applied to saiddifferential amplifier by way of said power supply terminals.
 6. Acircuit arrangement in accordance with claim 5, wherein said alternatingsignal voltage is applied in common mode to said power supply terminalswith a DC potential difference between said power supply terminalscorresponding to said operating voltage.
 7. A circuit arrangement inaccordance with claim 5, wherein said operating voltage from said powersupply is referenced to said alternating signal voltage.
 8. A circuitarrangement in accordance with claim 7, wherein said power supply isfloating and has a referencing input node for receiving a referencingpotential for said supply voltage is applied between a point of areference potential and said referencing input node.
 9. A circuitarrangement in accordance with claim 7, wherein said referencing inputnode is at a mid-potential point of said operating voltage.
 10. Acircuit arrangement in accordance with claim 7, wherein said referencinginput node is connected to one pole of said operating voltage.
 11. Acircuit arrangement in accordance with claim 10, wherein said one poleis coupled to a non-inverting input of said differential input.
 12. Acircuit arrangement in accordance with claim 8, wherein said output ofsaid differential amplifier provides an output signal with reference tosaid point of a reference potential.
 13. A circuit arrangement inaccordance with claim 12, wherein said operational amplifier is arrangedas a voltage follower with respect to said alternating signal voltage.14. A circuit arrangement in accordance with claim 13, wherein saidoperational amplifier is arranged as a voltage follower having apredetermined voltage gain.
 15. A circuit arrangement in accordance withclaim 14, wherein said output of said differential amplifier provides anoutput signal for a load coupled between said output and said point of areference potential.
 16. A circuit arrangement in accordance with claim15, wherein said output is coupled for negative feedback to saiddifferential input.
 17. A circuit arrangement in accordance with claim5, wherein said alternating signal voltage is applied in a common modeto said differential input, and is applied to said power supplyterminals of said operational amplifier with a DC potential differencebetween said power supply terminals corresponding to said operatingvoltage.
 18. A circuit arrangement in accordance with claim 17, whereinsaid output signal is representative of a superposition of saidrelatively small audio signal voltage including said DC component of agiven value and of said alternating signal voltage.
 19. A circuitarrangement in accordance with claim 5, wherein said alternating signalvoltage is provided by switching converter means.
 20. A circuitarrangement for transmitting to a remote receiver a relatively smallaudio signal voltage including a DC component of a given value, and arelatively large alternating signal voltage, said circuit arrangementcomprising an operational amplifier having a predeterminedamplification, having a differential input, an output, and a pair ofsupply terminals for receiving there between an operating voltage from apower supply, wherein said power supply is floating with respect to apoint of a reference potential; said differential amplifier is floatingrelative to said point of a reference potential:said audio signalvoltage is applied in a differential mode to said differential input;and said operating voltage from said power supply and said alternatingsignal voltage are superimposed and applied to said differentialamplifier by way of said power supply terminals.
 21. A circuitarrangement in accordance with claim 20, wherein said alternating signalvoltage is applied in common mode to said power supply terminals with aDC potential difference between said power supply terminalscorresponding to said operating voltage.
 22. A circuit arrangement inaccordance with claim 21, wherein said power supply has a referencinginput node for referencing a floating potential for said supply voltage,and wherein said alternating signal voltage is applied between a pointof a reference potential and said referencing input node.
 23. A circuitarrangement in accordance with claim 22, wherein said referencing inputnode is at a mid-potential point of said operating voltage.
 24. Acircuit arrangement in accordance with claim 23, wherein saidreferencing input node is connected at one pole of said operatingvoltage.
 25. A circuit arrangement in accordance with claim 10, whereinsaid one pole is connected to a non-inverting input of said differentialinput.
 26. A circuit arrangement in accordance with claim 25, whereinsaid output of said differential amplifier provides an output signalwith reference to said point of a reference potential.
 27. A circuitarrangement in accordance with claim 26, wherein said operationalamplifier is arranged as a voltage follower with respect to saidalternating signal voltage.
 28. A circuit arrangement in accordance withclaim 27, wherein said operational amplifier is arranged as a voltagefollower having a predetermined voltage gain.
 29. A circuit arrangementin accordance with claim 28, wherein said output is coupled for negativefeedback to said differential input.
 30. A circuit arrangement inaccordance with claim 20, wherein said alternating signal voltage isapplied in a common mode to said differential input, and is applied tosaid supply inputs of said operational amplifier with a DC potentialdifference between said power supply terminals corresponding to saidoperating voltage.
 31. A circuit arrangement in accordance with claim26, wherein said output signal is representative of a superposition ofsaid relatively small audio signal voltage including said DC componentof a given value and of said relatively large alternating signalvoltage.
 32. A circuit arrangement in accordance with claim 31, whereinsaid alternating signal voltage is provided by switching convertermeans.
 33. A circuit arrangement for supplying to a remote receivercircuit, a first, relatively small amplitude signal from the firstsignal source, including a DC component of a predetermined amount, as inthe transmission of an alternating speech signal, and a second,relatively large amplitude signal from a second signal source, as in thetransmission of an alternating ringing signal, said circuit arrangementcomprising an operational amplifier having a predetermined gain, havingfist and second input terminals for forming a differential input, havingfirst and second power supply terminals for receiving a supply voltagefrom a power supply source having first and second power supply outputterminals, and having an output terminal, whereinsaid first signalsource is coupled between said first and second input terminals; saidfirst and second power supply output terminals are coupled to respectiveones of said first and second power supply terminals; and said secondsignal source is coupled between a common node of said power supplysource and a point of a reference potential, whereby said power supplyoutput terminals are driven in common mode by said second signal withrespect to said point of a reference potential, and an output voltage isprovided between said output terminal and said point of a referencepotential.
 34. A circuit arrangement in accordance with claim 33,wherein said common node of said power supply source is connected to oneof said power supply output terminals.
 35. A circuit arrangement inaccordance with claim 34, wherein said common node of said power supplysource is connected to a point of potential intermediate the potentialsof said power supply output terminals.
 36. A circuit arrangement inaccordance with claim 34, wherein said common node of said power supplysource is connected to a point of potential substantially halfwaybetween the potentials of said power supply output terminals.
 37. Acircuit arrangement in accordance with claim 36, wherein said commonnode of said power supply source is connected to a non-inverting one ofsaid first and second input terminals of said differential input, saidoperational amplifier output terminal is coupled by way of impedancemeans to an inverting one of said first and second input terminals ofsaid differential input for providing negative feedback for setting saidoperational amplifier to operate at a relatively high gain level withrespect to said relatively small signal, and said operational amplifieroperates as a voltage follower with a relatively low gain with respectto said relatively large amplitude signal.
 38. A circuit arrangement inaccordance with claim 37, wherein said relatively low gain with respectto said relatively large amplitude signal is in the order of unity gain.39. Circuitry according to claim 1, characterized in that the highenergy alternating signal is a ringing alternating voltage forsignaling.